1. Field the Invention
This invention relates to a substrate drying apparatus for drying substrates, such as semiconductor wafers or LCD substrates, after the cleaning treatment thereof.
2. Description of the Related Art
In the manufacturing process of semiconductor devices, it is important to transfer wafers with no foreign materials to a place where they are next treated. Therefore, when each treatment has been finished, foreign materials, if any, are removed from the wafers to clean their surfaces. After the cleaning, the wafers are washed using ultrapure water, and then dried.
A vapor-using substrate drying apparatus is generally used to dry wafers since it can provide very cleaned wafers. In this apparatus, an organic solvent of a low boiling point, such as isopropyl alcohol (hereinafter referred to as "IPA") which has a boiling point of about 82.degree. C., is heated and evaporated. Each wafer is exposed to the resultant vapor (IPA vapor), and moisture thereon is replaced with IPA. The wafer is then transferred to the outside of the treatment vessel, where IPA attached thereto is again evaporated. Thus, the vapor using apparatus can provide wafers with dry and clean surfaces which are free from contamination materials such as dirt particles or chemicals.
Further, the conventional substrate drying apparatus of the vapor-using type is equipped with an electric resistance type sheathed heater or a cartridge heater-embedded hot plate. The hot plate is generally attached to the outer surface of the bottom of the treatment vessel of the apparatus, to indirectly heat IPA contained in the vessel. This is because IPA has high inflammability and hence may easily cause a fire accident. In other words, it is prohibited for safety's sake to directly heat IPA in the treatment vessel by an electric heater. Moreover, in the conventional apparatus, the electric heater is set to have a low capacity to avoid generation of an excessive amount of IPA which may occur due to disorder of a control system for the heater.
In light of the above, in the conventional drying apparatus, the heater indirectly heats IPA with a quartz glass wall or a stainless steel wall interposed therebetween. Accordingly, the thermal conductivity and the thermal responsiveness are inevitably low. This means that a great amount of time is required, after the start of heating, to generate a sufficient amount of IPA vapor to perform the drying treatment, and therefore that a great number of wafers cannot safely and speedily be dried.
In addition, since a plurality of wafers are treated at a time in the cleaning and drying treatments, it is necessary to reduce the amounts of consumed energy and IPA. In the conventional apparatuses, however, the control system employed therein for controlling the amount of IPA vapor has only a low responsiveness. Therefore, the amount of vapor necessary for the drying treatment must be kept at all times, with the result that the consumption amounts of energy and IPA cannot greatly be reduced.